Artificial intervertebral disc having a wave washer force restoring element

ABSTRACT

An artificial disc having a pair of opposing plates for seating against opposing vertebral bone surfaces, separated by a wave washer having a circumferential extent surrounding a central bore. Various wave washer embodiments disclosed include circumferential extents that are ring-shaped, spiral-shaped, straight, bowed, grooved, wavy, thinning, thickening, and slotted. Various central bores disclosed include simple bores and bores that form a curvate socket. Various plate embodiments disclosed include plates having, on inwardly facing surfaces, a flat surface, a circular recess, or a ball-shaped protuberance that is mateable with the curvate socket. The wave washers are disposable between the plates, through various disclosed couplings, so that the plates compress, rotate and angulate freely relative to one another, enabling the artificial disc to mimic a healthy natural intervertebral disc.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuing application of U.S. patentapplication Ser. No. 10/177,377 entitled “Artificial Intervertebral DiscHaving a Wave Washer Force Restoring Element”, filed Dec. 23, 2003,which is a continuing application of U.S. patent application Ser. No.09/906,117 entitled “Intervertebral Spacer Device Having a Wave WasherForce Restoring Element”, filed Jul. 16, 2001, and a continuingapplication of U.S. patent application Ser. No. 09/906,118 entitled“Intervertebral Spacer Device Having a Spiral Wave Washer ForceRestoring Element”, filed Jul. 16, 2001.

FIELD OF THE INVENTION

[0002] This invention relates generally to a spinal implant assembly forimplantation into the intervertebral space between adjacent vertebralbones to simultaneously provide stabilization and continued flexibilityand proper anatomical motion, and more specifically to such a devicethat utilizes a wave washer force restoring element.

BACKGROUND OF THE INVENTION

[0003] The bones and connective tissue of an adult human spinal columnconsists of more than 20 discrete bones coupled sequentially to oneanother by a tri-joint complex that consists of an anterior disc and thetwo posterior facet joints, the anterior discs of adjacent bones beingcushioned by cartilage spacers referred to as intervertebral discs.These more than 20 bones are anatomically categorized as being membersof one of four classifications: cervical, thoracic, lumbar, or sacral.The cervical portion of the spine, which comprises the top of the spine,up to the base of the skull, includes the first 7 vertebrae. Theintermediate 12 bones are the thoracic vertebrae, and connect to thelower spine comprising the 5 lumbar vertebrae. The base of the spine isthe sacral bones (including the coccyx). The component bones of thecervical spine are generally smaller than those of the thoracic spine,which are in turn smaller than those of the lumbar region. The sacralregion connects laterally to the pelvis. While the sacral region is anintegral part of the spine, for the purposes of fusion surgeries and forthis disclosure, the word spine shall refer only to the cervical,thoracic, and lumbar regions.

[0004] The spinal column is highly complex in that it includes thesemore than 20 bones coupled to one another, housing and protectingcritical elements of the nervous system having innumerable peripheralnerves and circulatory bodies in close proximity. In spite of thesecomplications, the spine is a highly flexible structure, capable of ahigh degree of curvature and twist in nearly every direction.

[0005] Genetic or developmental irregularities, trauma, chronic stress,tumors, and degenerative wear are a few of the causes that can result inspinal pathologies for which surgical intervention may be necessary. Avariety of systems have been disclosed in the art that achieveimmobilization and/or fusion of adjacent bones by implanting artificialassemblies in or on the spinal column. The region of the back that needsto be immobilized, as well as the individual variations in anatomy,determine the appropriate surgical protocol and implantation assembly.With respect to the failure of the intervertebral disc, the interbodyfusion cage has generated substantial interest because it can beimplanted laparoscopically into the anterior of the spine, thus reducingoperating room time, patient recovery time, and scarification.

[0006] Referring now to FIGS. 7 and 8, in which a side perspective viewof an intervertebral body cage and an anterior perspective view of apost implantation spinal column are shown, respectively, a more completedescription of these devices of the prior art is herein provided. Thesecages 10 generally comprise tubular metal body 12 having an externalsurface threading 14. They are inserted transverse to the axis of thespine 16, into preformed cylindrical holes at the junction of adjacentvertebral bodies (in FIG. 8 the pair of cages 10 are inserted betweenthe fifth lumbar vertebra (L5) and the top of the sacrum (S1)). Twocages 10 are generally inserted side by side with the external threading14 tapping into the lower surface of the vertebral bone above (L5), andthe upper surface of the vertebral bone (S1) below. The cages 10 includeholes 18 through which the adjacent bones are to grow. Additionalmaterials, for example autogenous bone graft materials, may be insertedinto the hollow interior 20 of the cage 10 to incite or accelerate thegrowth of the bone into the cage. End caps (not shown) are oftenutilized to hold the bone graft material within the cage 10.

[0007] These cages of the prior art have enjoyed medical success inpromoting fusion and grossly approximating proper disc height. It is,however, important to note that the fusion of the adjacent bones is anincomplete solution to the underlying pathology as it does not cure theailment, but rather simply masks the pathology under a stabilizingbridge of bone. This bone fusion limits the overall flexibility of thespinal column and artificially constrains the normal motion of thepatient. This constraint can cause collateral injury to the patient'sspine as additional stresses of motion, normally borne by the now-fusedjoint, are transferred onto the nearby facet joints and intervertebraldiscs. It would therefore, be a considerable advance in the art toprovide an implant assembly which does not promote fusion, but, rather,which nearly completely mimics the biomechanical action of the naturaldisc cartilage, thereby permitting continued normal motion and stressdistribution.

[0008] It is, therefore, an object of the invention to provide anintervertebral spacer that stabilizes the spine without promoting a bonefusion across the intervertebral space.

[0009] It is further an object of the invention to provide an implantdevice that stabilizes the spine while still permitting normal motion.

[0010] It is further an object of the invention to provide a device forimplantation into the intervertebral space that does not promote theabnormal distribution of biomechanical stresses on the patient's spine.

[0011] It is further an object of the invention to provide an artificialdisc that has an plate attachment device (for attaching the plates ofthe artificial disc to the vertebral bones between which the disc isimplanted) with superior gripping and holding strength upon initialimplantation and thereafter.

[0012] It is further an object of the invention to provide an artificialdisc plate attachment device that deflects during insertion of theartificial disc between vertebral bodies.

[0013] It is further an object of the invention to provide an artificialdisc plate attachment device that conforms to the concave surface of avertebral body.

[0014] It is further an object of the invention to provide an artificialdisc plate attachment device that does not restrict the angle at whichthe artificial disc can be implanted.

[0015] It is further an object of the invention to provide an artificialdisc that supports tension loads.

[0016] It is further an object of the invention to provide an artificialdisc that provides a centroid of motion centrally located within theintervertebral space.

[0017] Other objects of the invention not explicitly stated will be setforth and will be more clearly understood in conjunction with thedescriptions of the preferred embodiments disclosed hereafter.

SUMMARY OF THE INVENTION

[0018] The preceding objects are achieved by the invention, which is anartificial intervertebral disc or intervertebral spacer devicecomprising a pair of support members (e.g., spaced apart plates), eachwith an exterior surface. Because the artificial disc is to bepositioned between the facing surfaces of adjacent vertebral bodies, theplates are arranged in a substantially parallel planar alignment (orslightly offset relative to one another in accordance with properlordotic angulation) with the exterior surfaces facing away from oneanother. The plates are to mate with the vertebral bodies so as to notrotate relative thereto, but rather to permit the spinal segments toaxially compress and bend relative to one another in manners that mimicthe natural motion of the spinal segment. This natural motion ispermitted by the performance of a spring disposed between the securedplates, and the securing of the plates to the vertebral bone is achievedthrough the use of a vertebral body contact element including, forexample, a convex mesh attached to the exterior surface of each plate.Each convex mesh is secured at its perimeter, by laser welds, to theexterior surface of the respective plate. While domed in its initialundeflected conformation, the mesh deflects as necessary duringinsertion of the artificial disc between vertebral bodies, and, once theartificial disc is seated between the vertebral bodies, the mesh deformsas necessary under anatomical loads to reshape itself to the concavesurface of the vertebral endplate. Thus, the wire mesh is deformablyreshapeable under anatomical loads such that it conformably deflectsagainst the concave surface to securably engage the vertebral bodyendplate. Stated alternatively, because the wire mesh is convexly shapedand is secured at its perimeter to the plate, the wire mesh is biasedaway from the plate but moveable toward the plate (under a loadovercoming the bias; such a load is present, for example, as ananatomical load in the intervertebral space) so that it will securablyengage the vertebral body endplate when disposed in the intervertebralspace. This affords the plate having the mesh substantially superiorgripping and holding strength upon initial implantation, as comparedwith other artificial disc products. The convex mesh further provides anosteoconductive surface through which the bone may ultimately grow. Themesh preferably is comprised of titanium, but can also be formed fromother metals and/or non-metals. Inasmuch as the mesh is domed, it doesnot restrict the angle at which the artificial disc can be implanted. Itshould be understood that while the flexible dome is described hereinpreferably as a wire mesh, other meshed or solid flexible elements canalso be used, including flexible elements comprises of non-metals and/orother metals. Further, the flexibility, deflectability and/ordeformability need not be provided by a flexible material, but canadditionally or alternatively be provided mechanically or by othermeans.

[0019] To enhance the securing of the plates to the vertebral bones,each plate further comprises at least a lateral porous ring (which maybe, for example, a sprayed deposition layer, or an adhesive appliedbeaded metal layer, or another suitable porous coating known in theart). This porous ring permits the long-term ingrowth of vertebral boneinto the plate, thus permanently securing the prosthesis within theintervertebral space. The porous layer may extend beneath the domed meshas well, but is more importantly applied to the lateral rim of theexterior surface of the plate that seats directly against the vertebralbody.

[0020] The spring disposed between the plates provides a strongrestoring force when a compressive load is applied to the plates, andalso permits rotation and angulation of the two plates relative to oneanother. While a wide variety of embodiments are contemplated, apreferred spring includes a wave washer utilized as the restoring forceproviding element. In general, a wave washer is one of the strongestconfigurations for a spring, and is highly suitable for use as a forcerestoring providing subassembly for use in an intervertebral spacerelement that must endure considerable cyclical loading in an activehuman adult. A compressive load applied to the plates causes acorresponding compression of the wave washer, which is turn causes arestoring force to be applied to the plates. The wave washer deflectsappropriately under the load, only to spring back to its undeflectedshape upon the unloading.

[0021] In particular, in order for the overall device to mimic themechanical flexibility of the natural disc, it is desirable that thespring provide restoring forces that (1) are directed outward againstthe opposing plates, when a compressive load is applied to the plates;(2) that permit lateral bending and flexion and extension bending of theplates relative to parallel; (3) that do not permit lateral translationof the plates relative to one another during such bending; and (4) thatdo not substantially interfere with the rotation of the opposing platesrelative to one another. The wave washers disclosed herein provide suchfunctionality.

[0022] The wave washers of the invention have a circumferential extentsurrounding a central bore. The circumferential extent is concentricallywavy, such that the extent undulates along a concentric path around thecentral bore to form radially extending valleys and peaks, whilepreferably maintaining a constant radius. Stated equivalently withregard to the most basic wave washer embodiments of the invention, whichresemble traditional wave washers, the wave washer is a simple roundwasher having a circumferential extent that comprises a flat round ring,except that while maintaining a constant curvature of radius in theplane normally defined by the washer, the circumferential extent risesand falls in a wave-like curve. Whereas a standard (non-wave) washer hasa circumferential extent that is confined to the x-y plane, the wavewasher has a circumferential extent that extends in the x-y plane butundulates in the z-axis. Herein, the top and bottom of a wave washershall be defined as the planes defined by the lowest and highest pointsof the undulations, respectively. In some embodiments, thecircumferential extent is continuous (i.e., has no slots). In otherembodiments, the circumferential extent has at least one radiallyextending slot. In still other embodiments, the circumferential extenthas at least one radially extending and spiraling slot. The thickness ofthe circumferential extent; the frequency, amplitude, and configurationof the waves; and/or the number and configuration of the slots can bevaried to accommodate any desired application, inasmuch as varying thedimensions will affect the behavior of the wave washer in expansion andretraction.

[0023] The restoring force of a wave washer is proportional to theelastic properties of the material. As a compressive load is applied tothe wave washer, the forces are directed down onto the peaks and upagainst the valleys. A significant fraction of these forces areimmediately translated into hoop stresses that apply stresses directlytoward radially expanding the wave washer. This hoop stress is alsocounterbalanced by the material strength of the wave washer. The strainof the material causes a deflection in the height of the washer and aslight radial expansion. The slots in the slotted embodiments permit thecompressive load that is applied to the wave washer down onto the peaksand up against the valleys to cause the wave washer to deflect such thatthe slots close. Thus, a difference between a slotted washer and acontinuous washer is that the continuous washer responds to acompressive load by primarily deflecting radially (with a very highstress to deflection ratio), whereas the slotted washer primarilydeflects circumferentially, closing the slots (which is characteristicof a much lower stress to deflection ratio). Stated equivalently, a wavewasher responds to a compressive load by deflecting compressively, andeither radially or circumferentially. With at least one slot formed inthe washer, it expands and retracts far more elastically than acontinuous washer. It should be understood that wave washers other thanthose shown are contemplated by the invention, including but not limitedto wave washers having a circumferential extent that does not have auniformly wide radius.

[0024] As described above, the most basic wave washer of the inventionhas a circumferential extent that defines a circumference of 360 degrees(or less if the wave washer includes a radial slot that passescompletely through the circumferential extent). Another wave washerembodiment of the invention, instead of being ring-shaped, isspiral-shaped, having a circumferential extent that defines acircumference of more than 360 degrees, and preferably more than 720degrees, or more depending on the specific anatomical needs of thepatient. The undulations of the wave washer in the z-axis may be suchthat the arches are aligned, or misaligned. In yet another wave washerembodiment of the invention, instead of using a spiral-shaped wavewasher, multiple concentric ring-shaped wave washers can be used inconjunction with one another to achieve a similar functional result.

[0025] Still another wave washer embodiment of the invention is alsospiral-shaped, but has an amplitude of the undulations that decreases inthe radial direction. The wave washer thereby takes on the edge-onappearance of a spiral galaxy, having a thicker central portion, and aflatter edge. In this case, the restoring force varies according to thenumber of spirals of the washer and according to the number of spiralsthat are engaged (more radially distal spirals are engaged as thedeflection of the washer increases). More specifically, as a compressiveload is applied by a pair of plates against the top and bottom of aspiral wave washer, the forces are first directed against the peaks ofthe undulating waves at the center of the spiral, and are thenincreasingly directed against the peaks of the outer portions of thespiral. In a further wave washer embodiment of the invention, instead ofusing a spiral-shaped wave washer with radially decreasing undulationamplitudes, multiple concentric ring-shaped wave washers can be used inconjunction with one another, positioned so that those with smallerundulation amplitudes are more radially distant from the center of thegrouped washers, to achieve a similar functional result. It should beunderstood that in either of these types of embodiments, the wavewashers can be formed such that the undulation amplitudes increase,rather than decrease, with their radial distance from the center of thewasher, or such that the undulation amplitudes vary in size eitherrandomly or according to other patterns.

[0026] With regard to additional wave washer embodiments, changing theconfiguration of the circumferential extent in other ways modifies themagnitude of the compressive load support and restoring force providedby the wave washer. For clarity and conciseness, the othercircumferential extent configurations discussed herein are illustratedwith regard to wave washers having circumferential extents that arering-shaped (as opposed to spiral-shaped) and thicker compared to thewave washer embodiments summarized above (as those summarizedembodiments are illustrated), however it should be understood that theadditional circumferential extent variations discussed herein can beapplied individually or in various combinations to the spiral-shaped,concentric, and/or radially varying undulation amplitude configurations,without departing from the scope of the invention.

[0027] For example, a variety of circumferential extents are illustratedand discussed herein. In some embodiments, the circumferential extent isgenerally planar (e.g., the extent extends in a plane and all of thewaves undulate perpendicular to that plane). In other embodiments, thecircumferential extent is generally conical (e.g., the extent extends todefine a conical surface concentric with the central bore and the wavesundulate perpendicular to that surface at their respective positions onthe surface) and radially straight, such that the height of the wavewasher is linearly related to the radial width of the circumferentialextent. In still other embodiments, the circumferential extent isgenerally semispherical (e.g., the extent extends to define asemispherical surface concentric with the central bore and the wavesundulate perpendicular to that surface at their respective positions onthe surface) and radially bowed, such that the height of the wave washeris not linearly related to the radial width of the circumferentialextent (but rather the wave washer may, for example, be parabolic inshape). In still other embodiments, the circumferential extent extendsradially downwardly from the central bore. In still other embodiments,the circumferential extent is doubled, with a lower portion extendingradially downwardly from the central bore and an upper portion extendingradially upwardly from the central bore. By changing the circumferentialextent from a generally planar configuration to a generally conical orgenerally semispherical configuration, the resting height of the washeris increased and the radial expansion potential of the washer isincreased while the structural integrity of the washer is enhanced. Theshape and direction of the circumferential extent can be varied toaccommodate desired applications, inasmuch as varying the dimensionswill affect the behavior of the wave washer in expansion and retraction.

[0028] Also, for example, additional configurations of thecircumferential extent are possible, and are illustrated and discussedherein, to affect the behavior of the wave washer in expansion andretraction. In some embodiments, in addition to the concentric wavinesscommon to all of the wave washer embodiments, the circumferential extenthas at least one concentric or radial characteristic that alters theperformance of the wave washer in expansion and/or retraction. Morespecifically, in some embodiments, the circumferential extent is notonly concentrically wavy, but is also radially wavy. In otherembodiments, the circumferential extent is radially thinning (theportion of the extent near the central bore is thicker than the portionof the extent near the outer edge of the washer). In still otherembodiments, the circumferential extent is radially thickening (theportion of the extent near the central bore is thinner than the portionof the extent near the outer edge of the washer). In still otherembodiments, the circumferential extent is concentrically grooved,having grooves that are similarly dimensioned to one another regardlessof their relative radial distance from the central bore, or grooves thatvary in dimension from one another depending on their relative radialdistance from the central bore. These alterations, depending on theconfiguration, cause certain portions (e.g., grooved, thinner, or morewavy portions) of the circumferential extent to expand more readily thanother portions (e.g., non-grooved, thicker or less wavy portions).

[0029] It should be noted that with regard to the waves of the wavewashers of the invention, one or both of the depth and the width of eachwave can be (1) decreasing along the length of the wave from the outeredge of the washer toward the central bore, (2) increasing along thelength of the wave from the outer edge of the washer toward the centralbore, (3) uniform along the length of the wave from the outer edge ofthe washer toward the central bore, or (4) varied along the length ofeach wave from the outer edge of the washer toward the central bore,either randomly or according to a pattern. Moreover, it can be the casethat each wave is not formed similarly to one or more other waves, butrather one or more waves are formed in any of the above-mentionedfashions, while one or more other waves are formed in another of theabove-mentioned fashions or other fashions. It should be clear that anywave pattern can be implemented without departing from the scope of theinvention. By making the wave pattern non-uniform, certain portions ofthe circumferential extent give more readily than other portions, andtherefore the behavior of the wave washer in expansion and retractioncan be modified and/or controlled.

[0030] For disposing the wave washer (whichever wave washer embodimentis chosen for the clinical application) between the plates, each wavewasher embodiment has at least one feature suitable for this purpose,and the plates of the artificial disc comprise cooperating featuressuitable for this purpose. With regard to the wave washer features, eachwave washer embodiment has a central bore and at least one end thatexpands and retracts as described above. The central bore of some wavewasher embodiments forms a curvate socket on a narrow end of the wavewasher, for coupling with a ball-shaped protuberance on a plate asdescribed below.

[0031] With regard to the structure and coupling features of the plates,three plate embodiments are illustrated and described herein, althoughother suitable plate embodiments can be used with the invention. Each ofthe three plate embodiments has the above described convex mesh on itsoutwardly facing surface, although other vertebral body attachmentdevices and mechanisms can be used without departing from the scope ofthe invention. Each of the three plate embodiments has a differentinwardly facing surface from the other two plate embodiments. The firstplate embodiment has a flat inwardly facing surface that accepts afastener (e.g., a screw, plug, dowel or rivet; a rivet is used herein asan example) for rotatably securing thereto a narrow end of a wave washerhaving a circumferential extent that is generally conical or generallysemispherical, and/or that accepts a flanged (and preferably rotatable)fastener (e.g., a screw, plug, dowel, rivet, or spoked post; a rotatablespoked post is used herein as an example) for securing thereto a wavewasher having a circumferential extent that is generally planar. Thesecond plate embodiment has a circular recess on its inwardly facingsurface, for rotationally housing an end of a wave washer and allowingthe end to expand in unrestricted fashion when the wave washer iscompressed. The third plate embodiment has a semispherical (e.g.,ball-shaped) protuberance on its inwardly facing surface, for rotatablyand angulatably holding a narrow end of a wave washer, which narrow endincludes a curvate socket as described below.

[0032] The semispherical protuberance has an axial bore that receives adeflection preventing element (e.g., a rivet, plug, dowel, or screw; arivet is used herein as an example). Prior to the insertion of therivet, the ball-shaped protuberance can deflect radially inward (so thatthe ball-shaped protuberance contracts). The insertion of the riveteliminates the capacity for this deflection. The curvate socket, havinga substantially constant radius of curvature that is also substantiallyequivalent to the radius of the ball-shaped protuberance, accommodatesthe ball-shaped protuberance for free rotation and angulation once theball-shaped protuberance is disposed in the curvate socket, but in theball-shaped protuberance's undeflected state, the ball-shapedprotuberance cannot fit through the opening leading to the curvatesocket. Therefore, the deflectability of the ball-shaped protuberance,prior to the insertion of the rivet, permits the ball-shapedprotuberance to be inserted into the curvate socket. Subsequentintroduction of the rivet into the axial bore of the ball-shapedprotuberance prevents the ball-shaped protuberance from deflecting, andthus prevents the ball-shaped protuberance from escaping the socket.Thereby, the ball-shaped protuberance can be secured in the curvatesocket so that it rotates and angulates therein through a range ofangles, thus permitting the plates to rotate and angulate relative toone another through a corresponding range of angles equivalent to thefraction of normal human spine rotation and angulation (to mimic normaldisc rotation and angulation).

[0033] With the three plate embodiments, the various wave washerembodiments, and the several manners in which they may be coupledtogether, it is possible to assemble a variety of artificial discembodiments. Many examples are described herein, although manypermutations that are contemplated and encompassed by the invention arenot specifically identified herein, but are readily identifiable with anunderstanding of the invention as described. For example, any of thewave washers can be disposed between circular recesses of opposingplates. Also for example, all wave washers having a curvate socket canhave the curvate socket coupled with a ball-shaped protuberance on aplate. Also for example, all wave washers having a simple bore (i.e.,without a curvate socket) can have the simple bore coupled with a flatinwardly facing surface of a plate using a fastener (e.g., a rotatablespoked post or a screw or a rivet). Also for example, each wave washerhaving a wide end (e.g., wave washers having a circumferential extentthat is generally conical or generally semispherical) can be disposedwith its wide end in a circular recess of a plate, and a retainingelement (e.g., a shield) can be secured over the wave washer after ithas been placed in the circular recess to prevent the wave washer fromescaping the recess when a tension load is applied to the plates.

[0034] Each assembly enjoys spring-like performance with respect toaxial compressive loads, as well as long cycle life to mimic the axialbiomechanical performance of the normal human intervertebral disc. Thewave washer expands radially and/or circumferentially under acompressive load, only to spring back into its undeflected shape when itis unloaded. As the wave washer compresses and decompresses, the wallsof the circular recess of the second plate embodiment maintain the endof the wave washer within a prescribed boundary on the inwardly facingsurface of the plate. Certain assemblies withstand tension loads on theoutwardly facing surfaces, because (in embodiments having a generallyconical or generally semispherical extent) the shield retains the wideend in the circular recess and because (in embodiments using theball-shaped protuberance) the rivet in the axial bore prevents theball-shaped protuberance from deflecting, thus preventing it fromexiting the curvate socket and because (in embodiments in which thenarrow end of a wave washer is secured by a rivet or a rotatable spokedpost), the flanged portion of the rivet (or the spokes of the post)prevents the wave washer from escaping the circular recess. Accordingly,in such embodiments, once the plates are secured to the vertebral bones,the assembly will not come apart when a normally experienced tensionload is applied to the spine, similar to the tension-bearing integrityof a healthy natural intervertebral disc.

[0035] Assemblies having the ball-and-socket joint also provide acentroid of motion centrally located within the intervertebral space,because the plates are made rotatable and angulatable relative to oneanother by the ball-shaped protuberance being rotatably and angulatablycoupled in the curvate socket. The centroid of motion remains in theball-shaped protuberance, and thus remains centrally located between thevertebral bodies, similar to the centroid of motion in a healthy naturalintervertebral disc.

BRIEF DESCRIPTION OF THE DRAWINGS

[0036]FIGS. 1.1 through 1.7 show various embodiments of plates of theinvention for use in an artificial disc of the invention.

[0037]FIGS. 1.1 and 1.2 show a bottom plan view and a side cutaway view,respectively, of a plate having a flat surface on its inwardly facingsurface.

[0038]FIGS. 1.3 and 1.4 show a bottom plan view and a side cutaway view,respectively, of a plate having a circular recess on its inwardly facingsurface.

[0039]FIGS. 1.5 and 1.6 show a bottom plan view and a side cutaway view,respectively, of a plate having a ball-shaped protuberance on itsinwardly facing surface.

[0040]FIG. 1.7 shows a top plan view of any of the plates of FIGS. 1.1through 1.6 (all appear the same from this view).

[0041]FIGS. 2.1 through 2.6 show top views of various embodiments ofwave washers of the invention for use in an artificial disc of theinvention, to illustrate a variety of circumferential extentconfigurations and central bore configurations contemplated by theinvention

[0042]FIG. 2.1 shows a wave washer having a continuous circumferentialextent.

[0043]FIG. 2.2 shows a wave washer having a circumferential extent withradially extending slots.

[0044]FIG. 2.3 shows a wave washer having a circumferential extent withradially extending and spiraling slots.

[0045]FIG. 2.4 shows a wave washer having a continuous circumferentialextent and a curvate socket.

[0046]FIG. 2.5 shows a wave washer having a circumferential extent withradially extending slots and a curvate socket.

[0047]FIG. 2.6 shows a wave washer having a circumferential extent withradially extending and spiraling slots and a curvate socket.

[0048]FIGS. 3.1 through 3.14 show side cross-section views and sideviews of various embodiments of wave washers of the invention for use inan artificial disc of the invention, to illustrate additional varietiesof circumferential extent configurations and central bore configurationsof the invention.

[0049]FIGS. 3.1 and 3.8 show wave washers having a generally planarcircumferential extent.

[0050]FIGS. 3.2 and 3.9 show wave washers having a generally conical andradially straight circumferential extent.

[0051]FIGS. 3.3 and 3.10 show wave washers having a generallysemispherical and radially bowed circumferential extent.

[0052]FIGS. 3.4 and 3.11 show wave washers having a generally conicaland radially straight circumferential extent that has a lower downwardlyextending portion and an upper upwardly extending portion.

[0053]FIGS. 3.5 and 3.12 show wave washers having a generallysemispherical and radially bowed circumferential extent that has a lowerdownwardly extending portion and an upper upwardly extending portion.

[0054]FIGS. 3.6 and 3.13 show wave washers having a generally conicaland radially straight circumferential extent and a curvate socket.

[0055]FIGS. 3.7 and 3.14 show wave washers having a generallysemispherical and radially bowed circumferential extent and a curvatesocket.

[0056]FIGS. 4.1 through 4.15 show side cross-section views and top viewsof circumferential extents of various embodiments of wave washers, toillustrate additional varieties of circumferential extent configurationsof the invention.

[0057]FIG. 4.1 shows a generally straight circumferential extent that isradially wavy.

[0058]FIG. 4.2 shows a generally straight circumferential extent that isradially thinning.

[0059]FIG. 4.3 shows a generally straight circumferential extent that isradially thickening.

[0060]FIG. 4.4 shows a generally straight circumferential extent that isconcentrically grooved, with grooves that are similarly dimensioned toone another regardless of their relative radial distance from thecentral hub.

[0061]FIG. 4.5 shows a generally straight circumferential extent that isconcentrically grooved, with grooves that become smaller with a greaterradial distance of the groove from the central hub.

[0062]FIG. 4.6 shows a generally straight circumferential extent that isconcentrically grooved, with grooves that become larger with a greaterradial distance of the groove from the central hub.

[0063]FIG. 4.7 shows a generally bowed circumferential extent that isradially wavy.

[0064]FIG. 4.8 shows a generally bowed circumferential extent that isradially thinning.

[0065]FIG. 4.9 shows a generally bowed circumferential extent that isradially thickening.

[0066]FIG. 4.10 shows a generally bowed circumferential extent that isconcentrically grooved, with grooves that are similarly dimensioned toone another regardless of their relative radial distance from thecentral hub.

[0067]FIG. 4.11 shows a generally bowed circumferential extent that isconcentrically grooved, with grooves that become smaller with a greaterradial distance of the groove from the central hub.

[0068]FIG. 4.12 shows a generally bowed circumferential extent that isconcentrically grooved, with grooves that become larger with a greaterradial distance of the groove from the central hub.

[0069]FIG. 4.13 shows a wave washer having a circumferential extent withconcentric grooves having a concentrically varying width.

[0070]FIGS. 4.14 and 4.15 show a wave washer having a circumferentialextent with at least one wave that varies in width and depth along thelength of the wave.

[0071]FIGS. 5.1 through 5.6 show side views of various assembledartificial disc embodiments of the invention, with plates and shields ofthe invention in side cutaway view, but wave washers of the invention inside view.

[0072]FIG. 5.1 shows a wave washer having a generally planarcircumferential extent, disposed between circular recesses of opposingplates.

[0073]FIG. 5.2 shows a wave washer having a generally planarcircumferential extent, disposed between circular recesses of opposingplates and maintained within the circular recesses by rotatable spokedposts.

[0074]FIG. 5.3 shows a wave washer having a generally semisphericalcircumferential extent, disposed between circular recesses of opposingplates.

[0075]FIG. 5.4 shows a wave washer having a generally semisphericalcircumferential extent, rotatably secured by a flanged rivet to a flatsurface of an upper plate and its wide end seated within a circularrecess of a lower plate.

[0076]FIG. 5.5 shows a wave washer having a generally semisphericalcircumferential extent and a curvate socket, with its curvate socketcoupled to a ball-shaped protuberance of an upper plate and its wide endseated within a circular recess of a lower plate.

[0077]FIG. 5.6 shows a wave washer having two wide ends, with its topwide end seated within a circular recess of an upper plate, and itsbottom wide end seated within a circular recess of a lower plate.

[0078]FIG. 6.1 through 6.5 show perspective views of additional wavewashers of the invention, to illustrate additional varieties ofcircumferential extent configurations of the invention

[0079]FIG. 6.1 shows a wave washer having a ring-shaped circumferentialextent and a radial slot extending fully through the circumferentialextent.

[0080]FIG. 6.2 shows a wave washer having a spiral-shapedcircumferential extent.

[0081]FIG. 6.3 shows a plurality of concentrically disposed wavewashers, each having a continuous circumferential extent.

[0082]FIG. 6.4 shows a wave washer having a spiral-shapedcircumferential extent that has peaks and valleys of radiallydiminishing amplitude.

[0083]FIG. 6.5 shows a plurality of concentrically disposed wavewashers, each having a continuous circumferential extent, disposed suchthat wave washers having peaks and valley of greater amplitude areradially close to the center of the plurality.

[0084]FIG. 7 shows a side perspective view of a prior art interbodyfusion device.

[0085]FIG. 8 shows a front view of the anterior portion of thelumbo-sacral region of a human spine, into which a pair of interbodyfusion devices of FIG. 7 have been implanted.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0086] While the invention will be described more fully hereinafter withreference to the accompanying drawings, in which particular embodimentsand methods of implantation are shown, it is to be understood at theoutset that persons skilled in the art may modify the invention hereindescribed while achieving the functions and results of the invention.Accordingly, the descriptions that follow are to be understood asillustrative and exemplary of specific structures, aspects and featureswithin the broad scope of the invention and not as limiting of suchbroad scope. Like numbers refer to similar features of like elementsthroughout.

[0087] Referring now to FIGS. 1.1 through 1.7, various embodiments ofplates of the invention for use in an artificial disc of the inventionare shown in bottom plan views (FIGS. 1.1, 1.3, and 1.5), side cutawayviews (where cross-sectional areas and surfaces viewable behind them areshown) (FIGS. 1.2, 1.4, and 1.6), and a top plan view (FIG. 1.7). Morespecifically, FIGS. 1.1 and 1.2 show a bottom plan view and a sidecutaway view, respectively, of a first embodiment 100 a of a plate.FIGS. 1.3 and 1.4 show a bottom plan view and a side cutaway view,respectively, of a second embodiment 100 b of a plate. FIGS. 1.5 and 1.6show a bottom plan view and a side cutaway view, respectively, of athird embodiment 100 c of a plate. FIG. 1.7 shows a top plan view of anyof the plates 100 a-c (all appear the same from this view). As will bedescribed in greater detail below, depending on the type of wave washerused in a particular embodiment of an artificial disc of the invention,two plates selected (for the manner in which they cooperate with thetype of wave washer used in the embodiment) from these three embodimentswill be used as opposing plates of the embodiment. Some embodiments ofthe artificial disc use two plates of the same plate embodiment.

[0088] Each plate 100 a-c has an exterior surface 108 a-c. Because theartificial disc of the invention is to be positioned between the facingsurfaces of adjacent vertebral bodies, the two plates used in theartificial disc are disposed such that the exterior surfaces face awayfrom one another (as best seen in FIGS. 5.1 through 5.6, discussedbelow). The two plates are to mate with the vertebral bodies so as tonot rotate relative thereto, but rather to permit the spinal segments toaxially compress and bend relative to one another in manners that mimicthe natural motion of the spinal segment. This motion is permitted bythe performance of a wave washer (described below) disposed between thesecured plates. The mating of the plates to the vertebral bodies and theapplication of the wave washer to the plates are described below.

[0089] More particularly, each plate 100 a-c is a flat plate (preferablymade of a metal such as, for example, titanium) having an overall shapethat conforms to the overall shape of the respective endplate of thevertebral body with which it is to mate. Further, each plate 100 a-ccomprises a vertebral body contact element (e.g., a convex mesh 106 a-c)(preferably oval in shape) that is attached to the exterior surface 108a-c of the plate 100 a-c to provide a vertebral body contact surface.The mesh 106 a-c is secured at its perimeter, by laser welds, to theexterior surface 108 a-c of the plate 100 a-c. The mesh is domed in itsinitial undeflected conformation, but deflects as necessary duringinsertion of the artificial disc between vertebral bodies, and, once theartificial disc is seated between the vertebral bodies, deforms asnecessary under anatomical loads to reshape itself to the concavesurface of the vertebral endplate. This affords the plate having themesh substantially superior gripping and holding strength upon initialimplantation as compared with other artificial disc products. The meshfurther provides an osteoconductive surface through which the bone mayultimately grow. The mesh is preferably comprised of titanium, but canalso be formed from other metals and/or non-metals without departingfrom the scope of the invention.

[0090] Each plate 100 a-c further comprises at least a lateral ring 110a-c that is osteoconductive, which may be, for example, a sprayeddeposition layer, or an adhesive applied beaded metal layer, or anothersuitable porous coating. This porous ring permits the long-term ingrowthof vertebral bone into the plate, thus permanently securing theprosthesis within the intervertebral space. It shall be understood thatthis porous layer 110 a-c may extend beneath the domed mesh 106 a-c aswell, but is more importantly applied to the lateral rim of the exteriorsurface 108 a-c of the plate 100 a-c that seats directly against thevertebral body.

[0091] It should be understood that the convex mesh attachment devicesand methods described herein can be used not only with the artificialdiscs and artificial disc plates described or referred to herein, butalso with other artificial discs and artificial disc plates, including,but not limited to, those currently known in the art. Therefore, thedescription of the mesh attachment devices and methods being used withthe artificial discs and artificial disc plates described or referred toherein should not be construed as limiting the application and/orusefulness of the mesh attachment device.

[0092] With regard to the disposition of a wave washer between twoplates, each of the plates 100 a-c comprises features for applying thewave washer thereto, and the various application methods are describedbelow. More specifically, the first plate embodiment 100 a includes aninwardly facing surface 104 a that includes a flat surface 102 a thataccepts a fastener (e.g., a screw, plug, dowel or rivet; a rivet 114 ais used herein as an example) (shown in FIG. 5.4) for rotatably securinga narrow end of a wave washer thereto.

[0093] The second plate embodiment 100 b includes an inwardly facingsurface 104 b that includes a circular recess 102 b for rotationallyhousing an end of a wave washer and allowing the end to expand inunrestricted fashion when the wave washer is compressed, and theinwardly facing surface 104 b also accepts fasteners (e.g., screw,plugs, dowels, or rivets; rivets 116 b are used herein as examples)(shown in FIGS. 5.4 through 5.6) for securing a retaining element (e.g.,a shield 118 b) (the purpose and application of the shield are describedbelow and shown on FIGS. 5.4 through 5.6).

[0094] The third plate embodiment 100 c includes an inwardly facingsurface 104 c that includes an inwardly directed semispherical (e.g.,ball-shaped) protuberance 102 c. The ball-shaped protuberance 102 cincludes a series of slots 120 c that render the ball-shapedprotuberance 102 c radially compressible and expandable incorrespondence with a radial pressure (or a radial component of apressure applied thereto). The ball-shaped protuberance 102 c furtherincludes an axial bore 122 c that accepts a deflection preventingelement (e.g., a screw, plug, dowel, or rivet; a rivet 124 c is usedherein as an example) (shown in FIG. 5.5). (If a screw is used, theaxial bore can be threaded to accept it.) Prior to the insertion of therivet 124 c, the ball-shaped protuberance 102 c can deflect radiallyinward because the slots 120 c will narrow under a radial pressure. Theinsertion of the rivet 124 c eliminates the capacity for thisdeflection. Therefore, the ball-shaped protuberance 102 c, beforereceiving the rivet 124 c, can be compressed to seat in a curvate socketof a wave washer and, once the ball-shaped protuberance 102 c has beenseated in the curvate socket, the rivet 124 c can be inserted into theaxial bore 122 c to ensure that the ball-shaped protuberance 102 cremains held in the curvate socket. A hole can be provided in theopposing plate so that the interior of the device may be readilyaccessed if a need should arise.

[0095] The curvate socket has a substantially constant radius ofcurvature that is also substantially equivalent to the radius of theball-shaped protuberance with which it mates, so that when theball-shaped protuberance is secured therein, the ball-shapedprotuberance can rotate and angulate freely relative to the curvatesocket through a range of angles, thus permitting the opposing plates torotate and angulate freely relative to one another through acorresponding range of angles equivalent to the fraction of normal humanspine rotation and angulation (to mimic normal disc rotation andangulation). It should be understood that the specific dimensions of theball-shaped protuberance, the mechanism for radial compressibility ofthe ball-shaped protuberance, and the mechanism for preventing radialcompression of the ball-shaped protuberance are not limited to thoseshown, but rather can be varied and changed without departing from thescope of the invention.

[0096] Referring now to FIG. 6.1, an embodiment of a wave washer forcerestoring element of the invention is provided in a perspective view.The wave washer 610 comprises an undulating ring-shaped circumferentialextent 615 (preferably formed from a titanium alloy or stainless steel)having a radial slot 612 that extends fully though the circumferentialextent. The circumferential extent 615, while maintaining a constantradius, has undulations (a sinusoidal-type rising and falling of theextent) that create periodic peaks 613 and valleys 611.

[0097] It shall be understood that the wave washer 610 can also beprovided without a radial break or slot 612, and would thus becontinuous. The restoring force of a wave washer (whether continuous orslotted) is proportional to the elastic properties of the material, andthese are opposed as the compressive load is applied down onto the peaks613 and up against the valleys 611. In the case of a continuous wavewasher, the loads are translated into hoop stresses that apply stressesdirected toward radially expanding the washer. In the case of theradially slotted washer 610, the radial slot 612 permits the compressiveload that is applied to the washer (again, down onto the peaks 613 andup against the valleys 611) to cause the washer to radially expandwithout the build-up of hoop stresses. If the slotted wave washer 610 isradially constrained against such an expansion, the slot 612 is able toclose. The wave washer is therefore able to deflect downwardly withoutradially expanding. Stated equivalently, a difference between theradially slotted wave washer 610 of FIG. 6.1, and a continuous wavewasher, is that the continuous wave washer responds to a compressiveload by deflecting radially (with a very high stress to deflectionratio), whereas the radially slotted wave washer 610, when radiallyconstrained, deflects circumferentially, closing the slot 612 (which ischaracteristic of a much lower stress to deflection ratio).

[0098] With reference now to FIG. 6.2, another embodiment of a wavewasher force restoring element of the invention is provided inperspective view. The wave washer 620 comprises a circumferential extent625 formed from a spirally wound band of material (as above, a suitabletitanium alloy or stainless steel is preferable). As with thering-shaped wave washer 610 introduced above, the spirally wound wavewasher 620 includes a series of alternating and undulating peaks 623 andvalleys 621 that extend continuously around the spiral. The spiral wavewasher 620 in FIG. 6.2 shows the series of peaks 623 and valleys 621being radially aligned. Alternatively, it shall be understood that thepeaks and valleys may be non-aligned.

[0099] With reference to FIG. 6.3, yet another embodiment of a wavewasher force restoring element of the invention is provided inperspective view. A plurality of wave washers 630 a-c each comprises acircumferential extent 635 a-c that is ring-shaped, similar to the wavewasher 610 introduced above, but continuous (i.e., it has no radialslot). The wave washers 630 a-c are disposed relative to one another sothat they are concentric, with the wave washer 630 a having the smallestradius being surrounded by the wave washer 630 b having the next largestradius, which is in turn surrounded by a wave washer 630 c having aneven larger radius. The plurality of wave washers 630 a-c thereforeprovides a functionality similar to the spirally wound wave washer 620introduced above. It should be understood that more or fewer concentricwave washers can be similarly disposed without departing from the scopeof the invention. Further, although the peaks 633 a-c and valleys 631a-c of the wave washers 630 a-c are radially aligned, it shall beunderstood that alternatively, the peaks and valleys may be radiallynon-aligned in some embodiments.

[0100] With reference now to FIG. 6.4, still another embodiment of awave washer force restoring element of the invention is provided inperspective view. The wave washer 640 comprises a circumferential extent645 that is spirally would, similar to the wave washer 620 introducedabove, but in which the amplitudes of the peaks 643 and valleys 641 areradially diminishing. This conformation permits a non-linearload-deflection profile that more closely mimics the load-deflectionperformance of a natural disc. The spiral wave washer 640 in FIG. 6.4shows the series of peaks 643 and valleys 641 being radiallynon-aligned. Alternatively, it shall be understood that the peaks andvalleys may be radially aligned.

[0101] With reference to FIG. 6.5, yet another embodiment of a wavewasher force restoring element of the invention is provided inperspective view. A plurality of wave washers 650 a-c, formed anddisposed similarly to the plurality of wave washers 650 a-c introducedabove in that each comprises a continuous circumferential extent 655 a-cthat is ring-shaped, and in that they are disposed relative to oneanother so that they are concentric, with the wave washer 650 a havingthe smallest radius being surrounded by the wave washer 650 b having thenext largest radius, which is in turn surrounded by a wave washer 650 chaving an even larger radius. However, in this embodiment, the innerwave washer 650 a has peaks 653 a and valleys 651 a with amplitudessmaller than the amplitudes of the peaks 653 b and valleys 651 b of themiddle wave washer 650 b, which in turn have amplitudes smaller than theamplitudes of the peaks 653 c and valleys 651 c of the outer wave washer650 c. That is, the amplitudes of the peaks and valleys of the group ofwave washers 650 a-c decrease with the greater radial distance of thewasher from the inner washer. The plurality of wave washers 650 a-ctherefore provides a functionality similar to the spirally wound wavewasher 640 introduced above. It should be understood that more or fewerconcentric wave washers can be similarly disposed without departing fromthe scope of the invention. Further, although the peaks 653 a-c andvalleys 651 a-c of the wave washers 650 a-c are radially aligned, itshall be understood that alternatively, the peaks and valleys may beradially non-aligned in some embodiments.

[0102] With regard to additional wave washer embodiments, changing theconfiguration of the circumferential extent in other ways modifies themagnitude of the compressive load support and restoring force providedby the wave washer. For clarity and conciseness, the othercircumferential extent configurations discussed hereinbelow areillustrated with regard to wave washers having circumferential extentsthat are ring-shaped (as opposed to spiral-shaped) and thicker comparedto the wave washer embodiments summarized above (as those summarizedembodiments are illustrated), however it should be understood that theadditional circumferential extent variations discussed herein can beapplied individually or in various combinations to the spiral-shaped,concentric, and/or radially decreasing undulation amplitudeconfigurations, without departing from the scope of the invention.

[0103] Referring now to FIGS. 2.1 through 2.6, top views of variousadditional embodiments of wave washers of the invention for use in anartificial disc of the invention are shown to illustrate a variety ofadditional wave washer configurations and central bore configurationsthat are merely a subset of the wave washer configurations and centralbore configurations contemplated by the invention. More specifically,each wave washer (e.g., 200 a-u) has a circumferential extent (e.g., 202a-u) surrounding a central bore (e.g., 206 a-u). The circumferentialextent is concentrically wavy, such that the extent undulates along aconcentric path around the central bore to form radially extendingvalleys (e.g., 208 a-g) and peaks (e.g., 210 a-g) (best shown byexamples on FIGS. 3.8 through 3.14, discussed below) while preferablymaintaining a constant radius. In some embodiments (e.g., 200 a-g), thecircumferential extent (e.g., 202 a-g) is continuous (i.e., has noslots). In other embodiments (e.g., 200 h-n), the circumferential extent(e.g., 202 h-n) has radially extending slots (e.g., 212 h-n). In stillother embodiments (e.g., 200 o-u), the circumferential extent (e.g., 202o-u) has radially extending and spiraling slots (e.g., 212 o-u). Thefrequency, amplitude, and configuration of the waves and/or the numberand configuration of the slots can be varied to accommodate any desiredapplication, inasmuch as varying the dimensions will affect the behaviorof the wave washer in expansion and retraction.

[0104] The restoring force of a wave washer is proportional to theelastic properties of the material. As a compressive load is applied tothe wave washer, the forces are directed down onto the peaks and upagainst the valleys. A significant fraction of these forces areimmediately translated into hoop stresses that apply stresses directlytoward radially expanding the wave washer. This hoop stress is alsocounterbalanced by the material strength of the wave washer. The strainof the material causes a deflection in the height of the washer and aslight radial expansion. The slots in the slotted embodiments permit thecompressive load that is applied to the wave washer down onto the peaksand up against the valleys to cause the wave washer to deflect such thatthe slots close. Thus, a difference between a slotted washer and acontinuous washer is that the continuous washer responds to acompressive load by primarily deflecting radially (with a very highstress to deflection ratio), whereas the slotted washer deflectsprimarily circumferentially, closing the slots (which is characteristicof a much lower stress to deflection ratio). Stated equivalently, a wavewasher responds to a compressive load by deflecting compressively andeither radially or circumferentially. With at least one slot formed inthe washer, it expands and retracts far more elastically than acontinuous washer. It should be understood that wave washers other thanthose shown are contemplated by the invention, including but not limitedto wave washers having a circumferential extent that does not have auniformly wide radius.

[0105] With regard to the central bore configurations 206 a-u shown onFIGS. 2.1 through 2.6, these are discussed in greater detail below withreference to FIGS. 5.1 through 5.6 regarding methods of applying thewave washers to the plates discussed above. However, for properlyunderstanding the discussions of FIGS. 3.1 through 3.14 and 4.1 through4.15 below, it is important to summarize here that some wave washerembodiments (e.g., 200 a-e,h-l,o-s) have a simple bore (e.g., 206a-e,h-l,o-s), and other wave washer embodiments (e.g., 200 f-g,m-n,t-u)have a bore that forms a curvate socket (e.g., 206 f-g,m-n,t-u) of atype described above with regard to being mateable with thesemispherical protuberance described above.

[0106] Referring now also to FIGS. 3.1 through 3.14, side cross-sectionviews (where only the cross-sectional area is shown) and correspondingside views (some with side cross-section views shown in phantom forclarity) of various embodiments of wave washers are shown to illustrateadditional varieties of wave washer configurations and central boreconfigurations that are merely a subset of the wave washerconfigurations and central bore configurations contemplated by theinvention. The side cross-sections are taken along cut lines A1-A1′,F1-F1′, H-H′, M-M′, O-O′, and T-T′ on FIGS. 2.1 through 2.6, asapplicable, and the side views are taken along cut lines A2-A2′ andF2-F2′ on FIGS. 2.1 and 2.4, as applicable.

[0107] It should be understood that the use of multiple referencenumbers for various elements are used throughout the figures to indicatewhere a single view illustrates more than one wave washer embodiment,given that some wave washers look similar from certain views but notsimilar from other views. This has been done to consolidateillustrations for conciseness and clarity. For example, FIGS. 3.1through 3.5 illustrate wave washer embodiments that from a top viewappear as any of FIGS. 2.1 through 2.3. Also, for example, FIGS. 3.6 and3.7 illustrate wave washer embodiments that from a top view appear asany one of FIGS. 2.4 through 2.6. Stated alternatively, each of FIGS.3.1 through 3.7 is not a side cross-section view that is associated withonly one of the top views of FIGS. 2.1 through 2.6, but rather isassociatable with more than one of the top views of FIGS. 2.1 through2.6. And, for example, FIGS. 3.8 through 3.12 are side viewscorresponding respectively to the side cross-section views of FIGS. 3.1through 3.5, but only with regard to certain wave washer embodiments(e.g., 200 a-e), as noted by reference numbers, and FIGS. 3.13 and 3.14are side views corresponding respectively to the side cross-sectionviews of FIGS. 3.6 and 3.7, but only with regard to certain wave washerembodiments (e.g., 200 f-g), as noted by reference numbers. It should beunderstood, however, that certain configurations of wave washerembodiments (e.g., 200 h-l,o-s) would have similar side view appearancesas FIG. 3.8 through 3.12, and that certain configurations of wave washerembodiments (e.g., 200 m-n,t-u) would have similar side view appearancesas FIG. 3.13 through 3.14, except for the presentation of straight orspiral slots, as applicable.

[0108] More specifically, FIG. 3.1 shows a configuration where thecircumferential extent of the wave washer (e.g., 200 a,h,o) is generallyplanar (e.g., the extent extends in a plane and all of the wavesundulate perpendicular to that plane). FIGS. 3.2, 3.4, and 3.6 showconfigurations where the circumferential extent of the wave washer(e.g., 200 b,d,f,i,k,m,p,r,t) is generally conical (e.g., the extentextends to define a conical surface concentric with the central bore andthe waves undulate perpendicular to that surface at their respectivepositions on the surface) and radially straight, such that the height ofthe wave washer is linearly related to the radial width of thecircumferential extent. FIGS. 3.3, 3.5, and 3.7 show configurationswhere the circumferential extent of the wave washer (e.g., 200c,e,g,j,l,n,q,s,u) is generally semispherical (e.g., the extent extendsto define a semispherical surface concentric with the central bore andthe waves undulate perpendicular to that surface at their respectivepositions on the surface) and radially bowed, such that the height ofthe wave washer is not linearly related to the radial width of thecircumferential extent (but rather the wave washer may, for example, beparabolic in shape). FIGS. 3.2, 3.3, 3.6 and 3.7 show configurations inwhich the circumferential extent of the wave washer (e.g., 200b,c,f,g,i,j,m,n,p,q,t,u) extends radially downwardly from the centralbore. FIGS. 3.4 and 3.5 show configurations in which the circumferentialextent of the wave washer (e.g., 200 d,e,k,l,r,s) is doubled, with alower portion extending radially downwardly from the central bore and anupper portion extending radially upwardly from the central bore.

[0109] Further with regard to the central bores shown in top views onFIGS. 2.1 through 2.6, these are shown in side cross-section views inFIGS. 3.1 through 3.7, with some also shown in side cross-section viewsin phantom in FIGS. 3.13 and 3.14. More specifically, simple bores(e.g., 206 a-e,h-l,o-s) are shown in side cross-section views in FIGS.3.1 through 3.5. Bores that form curvate sockets (e.g., 206 f-g,m-n,t-u)are shown in side cross-section views in FIGS. 3.6 and 3.7 and some ofthose (e.g., 206 f-g) are also shown in side cross-section views inphantom in FIGS. 3.13 and 3.14.

[0110] Referring now also to FIGS. 4.1 through 4.12, side cross-sectionviews (where only the cross-sectional area is shown) of circumferentialextents (e.g., 202 aa-II) of various embodiments of wave washers areshown to illustrate additional varieties of wave washer configurationsthat are merely a subset of the wave washer configurations contemplatedby the invention. The side cross-sections are taken from the inner edgeof the circumferential extent (i.e., the edge of the central bore of thewave washer) radially to the outer edge of the circumferential extent.It should be understood that with regard to the remaining structure ofthe wave washers having the illustrated circumferential extents, thewave washers can share all or some of the features (e.g., boreconfigurations, double extent configurations, slot configurations, etc.)of the other wave washer embodiments discussed herein, and/or havefeatures that are different and/or configured differently.

[0111] More specifically, FIGS. 4.1 through 4.12 show configurationswhere the circumferential extent of the wave washer is generally conical(FIGS. 4.1 through 4.6) (the waves undulate about a conical surfaceconcentric with the central bore) and radially straight, such that theheight of the wave washer is linearly related to the radial width of thecircumferential extent, or generally semispherical (FIGS. 4.7 through4.12) (the waves undulate about a semispherical surface concentric withthe central bore) and radially bowed, such that the height of the wavewasher is not linearly related to the radial width of thecircumferential extent, but additionally have at least one concentric orradial characteristic (in addition to the concentric waviness common toall of the wave washer embodiments) that alters the performance of thewave washer in expansion and/or retraction. For example, thecircumferential extents in FIGS. 4.1 and 4.7 are not only concentricallywavy, but are also radially wavy. Also for example, the circumferentialextents in FIGS. 4.2 and 4.8 are radially thinning (the portion of theextent near the central bore is thicker than the portion of the extentnear the outer edge of the washer). Also for example, thecircumferential extents in FIGS. 4.3 and 4.9 are radially thickening(the portion of the extent near the central bore is thinner than theportion of the extent near the outer edge of the washer). Also forexample, the circumferential extents in FIGS. 4.4, 4.5, 4.6, 4.10, 4.11and 4.12 are concentrically grooved, having grooves that are similarlydimensioned to one another regardless of their relative radial distancefrom the central bore (FIGS. 4.4 and 4.10), or grooves that vary indimension from one another depending on their relative radial distancefrom the central bore (FIGS. 4.5, 4.6, 4.11 and 4.12). For example, thewidth and depth of the grooves in FIG. 4.5 and the grooves in FIG. 4.11become smaller with the greater radial distance of the groove from thecentral bore. And, for example, the width and depth of the grooves inFIG. 4.6 and the grooves in FIG. 4.12 become larger with the greaterradial distance of the groove from the central bore.

[0112] In some embodiments, at least one dimension of a concentricgroove (such as, for example, the width and/or depth) can be applied tovary concentrically across the circumferential extent. FIG. 4.13 showsone example of a configuration where two concentric grooves 211 v, 212v, each concentrically varying in width, are applied to thecircumferential extent 202 v of a wave washer 200 v.

[0113] It should be noted that with regard to the waves of the wavewashers of the invention, one or both of the depth and the width of eachwave can be (1) decreasing along the length of the wave from the outeredge of the washer toward the central bore, (2) increasing along thelength of the wave from the outer edge of the washer toward the centralbore, (3) uniform along the length of the wave from the outer edge ofthe washer toward the central bore, or (4) varied along the length ofeach wave from the outer edge of the washer toward the central bore,either randomly or according to a pattern. A wave washer embodiment 200w having a circumferential extent 202 w, as an example of case (1), isshown in top view in FIG. 4.14 (with dashed lines identifying thetangents of the adjacent peaks that define the wave) and incircumferential extent side cutaway view in FIG. 4.15 (taken along cutlines W-W′ in FIG. 4.14), where both the width and depth of a wave 213 wvary along the length of the wave. Moreover, it can be the case thateach wave is not formed similarly to one or more other waves, but ratherone or more waves are formed in any of the above-mentioned fashions,while one or more other waves are formed in another of theabove-mentioned fashions or other fashions. It should be clear that anywave pattern can be implemented without departing from the scope of theinvention.

[0114] It should be understood that the circumferential extentscontemplated by the invention include, but are not limited to, thosehaving only one concentric or radial characteristic at a time. The useof more than one concentric or radial characteristic per arm iscontemplated, as well as the use of concentric and radialcharacteristics simultaneously. Further, it is contemplated that somewave washer embodiments will use only a radially straightcircumferential extent, some wave washer embodiments will use only aradially bowed circumferential extent, and some wave washer embodimentsthat will use a circumferential extent that is radially straight in someportions and radially bowed in other portions.

[0115] Each of the wave washers is suitable for disposition between twoopposing plates of the invention. As noted above, and as discussed ingreater detail below, depending on the type of wave washer used in theparticular embodiment of the artificial disc of the invention, the twoplates are selected (for the manner in which they cooperate with thetype of wave washer used in the embodiment) from the three plateembodiments, for use as opposing plates of the embodiment. Someembodiments of the artificial disc use two plates of the same plateembodiment. In each embodiment, the plates are made rotatable andangulatable relative to one another (to mimic the functionality of ahealthy natural intervertebral disc) by having a wave washer between theplates, and/or by the manner in which the wave washer is secured to oneor both of the plates. Further in each embodiment, the same couplings,and/or through the use of additional coupling elements (e.g., shields,rivets, and/or rotatable spoked posts), enable the artificial discembodiments to withstand tension loading (to mimic the functionality ofa healthy natural intervertebral disc). Further in embodiments having awave washer, the wave washer enables the artificial disc embodiments toaxially compress and axially restore (to mimic the functionality of ahealthy natural intervertebral disc).

[0116] Referring now also to FIGS. 5.1 through 5.6, these figures showside views of various assembled artificial disc embodiments contemplatedby the invention. The side views show the plates in side cutaway view,but the wave washers in side view (with primary cross-sections andcouplings in phantom in some figures for clarity). It should beunderstood that the illustrated embodiments do not encompass allembodiments contemplated by the invention, but rather were selected forillustration purposes to show how the features of the variousillustrated plate embodiments cooperate with corresponding features ofthe various illustrated wave washer embodiments, when the wave washersare disposed between opposing plates of the invention. While onlycertain assembled artificial disc embodiments are shown, it should beunderstood that wave washers not shown but having like plate couplingfeatures can be secured to cooperating plates in the manner illustrated,in various permutations and combinations, and the same have beenwithheld from illustration for purposes of conciseness and clarity onlyto avoid duplicative illustration that would visually reiterate thatwhich can be understood from the descriptions and illustrations herein.

[0117] For example, any of the wave washers can be disposed betweencircular recesses on inwardly facing surfaces of opposing plates (e.g.,the circular recess 102 b on the inwardly facing surface 104 b of plate100 b). FIGS. 5.1 and 5.2 illustrate this disposition with wave washers(e.g., 200 a) having a circumferential extent that is generally planar(see, e.g., FIGS. 3.1 and 3.8). (It should be understood that any of thewave washer embodiments of FIGS. 6.1 through 6.5, and similarembodiments, can be substituted for the wave washer 200 a in FIGS. 5.1and 5.2 and be similarly disposed as shown and/or coupled as shown withplates having circular recesses on inwardly facing surfaces to formadditional artificial disc embodiments not specifically illustrated.)FIG. 5.3 illustrates this disposition with a wave washer (e.g., 200 c)having a circumferential extent that is generally semispherical (see,e.g., FIGS. 3.3 and 3.10), although the same disposition can be madewith a wave washer (e.g., 200 b) having a circumferential extent that isgenerally conical (see, e.g., FIGS. 3.2 and 3.9). FIG. 5.6 illustratesthis disposition with a wave washer (e.g., 200 e) having a doubledcircumferential extent that forms two generally semispherical portionsand opposing wide ends (see, e.g., FIGS. 3.5 and 3.12), although thesame disposition can be made with a wave washer (e.g., 200 d) having adoubled circumferential extent that forms two generally conical portionsand opposing wide ends (see, e.g., FIGS. 3.4 and 3.11). In each of theseassemblies, each end of the wave washer fits within a respectivecircular recess 102 b with room to expand when the wave washer is undercompression. Because the diameter of the circular recess is greater thanthe diameter of the wave washer, unrestrained rotation of the wavewasher relative to the plate having the circular recess is enabled, andcompressive loading of the artificial disc (and therefore the wavewasher) results in an unrestrained deflection of the wave washer, bothas necessary for proper anatomical response. Further in each of theseand similarly constructed assemblies, the plates are rotatable relativeto one another because the ends of the wave washer can rotate withrespect to the plate having the circular recess in which the end seatsas indicated above. Further, the plates are angulatable relative to oneanother because the waves of the wave washer can individually compressand restore, enabling one side of the circumferential extent to compressand restore as the plates angulate relative to one another, while otherportions of the circumferential extent do not.

[0118] Additional components can be applied in these assemblies in orderto prevent removal of the wave washer from the circular recess(es) whenthe artificial disc is loaded in tension. As an initial matter, ifrotation of a wave washer with respect to one of the plates is notdesirable, a simple fastener (e.g., a screw, plug, dowel or rivet) canbe used to secure the circumferential extent of the wave washer to acircular recess or a flat surface of an inwardly facing surface of aplate so that the wave washer can still compress and decompress, butcannot rotate with respect to the plate to which it is attached.Alternatively, FIG. 5.2 illustrates an example of how a wave washer(e.g., 200 a) having a circumferential extent that is generally planarcan be rotationally maintained between circular recesses. Opposingrotatable posts 114 b (each having at least one spoke 113 b extendinglaterally from an end of the post 114 b) can be rotatably installed, oneto each of the plates, so that the spokes align with the peaks andvalleys of the wave washer, and the post is rotatable with respect tothe plate. More specifically, an upper spoked post is applied with itspost portion through the bore and its spokes bearing under the peaks tocapture the peaks between the spokes and the upper plate, and a lowerspoked post is applied with its post portion through the bore and itsspokes bearing over the valleys to capture the peaks between the spokesand the lower plate. In this manner, the wave washer is held againstboth of the plates so that the assembly maintains its integrity under atension load while still permitting the washer to compress. It should beunderstood that one or both of the spoked posts can alternatively oradditionally be formed from multiple parts, in order to facilitate easyconstruction of the assembly. It should also be understood that otherflanged fasteners can be used instead of a spoked post.

[0119] With regard to preventing the removal of the wide ends of wavewashers (e.g., 200 b-g) having generally conical or generallysemispherical circumferential extents from the circular recess(es) whenthe artificial disc is loaded in tension, FIGS. 5.4 through 5.6illustrate a retaining element (e.g., a shield 118 b) that can be placedover the wave washer and secured by fasteners (e.g., screws, plugs,dowels, or rivets; rivets 116 b are used herein as examples). The shield118 b can have a central hole 120 b through which the curvate socket(discussed below with regard to FIG. 5.5) and the ball-shapedprotuberance (discussed below with regard to FIG. 5.5) can pass toaccommodate efficient assembly of the artificial disc. The shield 118 bcan alternatively or additionally be formed from multiple shield parts,which would be useful, for example, in embodiments where no part of thewave washer can pass through the central hole 120 b (see, e.g., theembodiment of FIG. 5.6, discussed below).

[0120] A wave washer that has a simple central bore (see, e.g., FIGS.2.1 through 2.3) and a circumferential extent that is generally conical(see, e.g., FIGS. 3.2 and 3.9) or generally semispherical (see, e.g.,FIGS. 3.3 and 3.10) can be disposed with its wide end against a circularrecess on an inwardly facing surface of a plate (e.g., the circularrecess 102 b on the inwardly facing surface 104 b of plate 100 b) asdescribed above, and its narrow end rotatably secured to a flat surfaceon an inwardly facing surface on an opposing plate (e.g., the flatsurface 102 a on the inwardly facing surface 104 a of plate 100 a). Asshown in FIG. 5.4, the narrow end of the wave washer (e.g., 200 b-c) canbe rotatably secured to the flat surface 104 a with a flanged fastener(e.g., a flanged screw, plug, dowel or rivet; a flanged rivet 114 a isused herein as an example) passing through the central bore of the wavewasher and secured to the flat surface 104 a of the plate 100 a. Theflanged rivet 114 a has a flanged portion at the end of a post portion.The post portion has a diameter smaller than the diameter of the bore,and a length that is longer than the thickness of the wave washer extentsurrounding the central bore, and the flanged portion has a diametergreater than the diameter of the bore. Therefore, upon application ofthe rivet 114 a, the wave washer is secured to the plate 100 a so thatit can still rotate with respect to the plate 100 a. (A threaded bore inthe plate can also be used in conjunction with a similarly flanged screwto achieve the same functionality.) As also discussed above with regardto the securing of the wide end of the wave washer, the plates aresecondarily rotatable relative to one another because the wide end ofthe wave washer can rotate with respect to the plate having the circularrecess in which the wide end seats. Further, the plates are angulatablerelative to one another because the waves of the wave washer canindividually compress and restore, enabling one side of thecircumferential extent to compress and restore as the plates angulaterelative to one another, while other portions of the circumferentialextent do not.

[0121] A wave washer that has a central bore that forms a curvate socket(see, e.g., FIGS. 2.4 through 2.6) and a circumferential extent that isgenerally conical (see, e.g., FIGS. 3.6 and 3.13) or generallysemispherical (see, e.g., FIGS. 3.7 and 3.14) can be disposed with itswide end against a circular recess on an inwardly facing surface of aplate (e.g., the circular recess 102 b on the inwardly facing surface104 b of plate 100 b) as described above, and its narrow end rotatablyand angulatably coupled with a semispherical protuberance on an inwardlyfacing surface on an opposing plate (e.g., the ball-shaped protuberance102 c on the inwardly facing surface 104 c of plate 100 c). As shown inFIG. 5.5, the central bore of such a wave washer (e.g., 200 f-g)preferably forms a curvate socket (e.g., 206 f-g,m-n,t-u) within whichthe ball-shaped protuberance 102 c is securable for free rotation andangulation through a range of angles. The structure of the curvatesocket and the coupling of the ball-shaped protuberance with the curvatesocket are as described above. As noted above, a deflection preventingelement (e.g., a screw, plug, dowel, or rivet 124 c) applied to theaxial bore 122 c after the ball-shaped protuberance 102 c has beeninserted into the curvate socket prevents the deflection of theball-shaped protuberance 102 c so that it does not escape the curvatesocket. The plates are rotatable relative to one another primarilybecause the ball-shaped protuberance rotates freely within the curvatesocket, and secondarily because the wide end of the wave washer canrotate with respect to the plate having the circular recess in which thewide end seats (discussed below). Also, the plates are angulatablerelative to one another primarily because the ball-shaped protuberanceangulates freely within the curvate socket, and secondarily because thewaves of the wave washer can individually compress and restore, enablingone side of the circumferential extents to compress and restore as theplates angulate relative to one another, while other portions of thecircumferential extent do not.

[0122] In embodiments having a ball-and-socket joint as described above,because the ball-shaped protuberance is held within the curvate socketby a rivet in the axial bore preventing radial compression of theball-shaped protuberance, the artificial disc can withstand tensionloading of the plates, as necessary for proper anatomical response. Moreparticularly, when a tension load is applied to the plates, theball-shaped protuberance in the curvate socket seeks to radiallycompress to fit through the opening of the curvate socket. However, therivet in the axial bore of the ball-shaped protuberance prevents theradial compression, thereby preventing the ball-shaped protuberance fromexiting the curvate socket. Further, in embodiments that have a wavewasher with a generally conical or generally semisphericalcircumferential extent, as the wide end of the wave washer seeks toescape the circular recess of the plate, the rivets holding the shieldin place over the wave washer prevent the shield from separating fromthe plate when the wave washer presses against the inner surface of theshield. Further, in embodiments where the narrow end of the wave washeris rotatably secured against a plate by a rivet, the flanged portion ofthe rivet prevents the separation of the narrow end of the wave washer.Therefore, the assembly does not come apart under normally experiencedtension loads. This ensures that no individual parts of the assemblywill pop out or slip out from between the vertebral bodies when thepatient stretches or hangs while exercising or performing otheractivities. Thus, in combination with the securing of the plates to theadjacent vertebral bones via the mesh domes, the disc assembly has anintegrity similar to the tension-bearing integrity of a healthy naturalintervertebral disc.

[0123] Further, because the plates in some embodiments are madeangulatable relative to one another by the ball-shaped protuberancebeing rotatably and angulatably coupled in a curvate socket, the discassembly provides a centroid of motion within the ball-shapedprotuberance. Accordingly, in those embodiments, the centroid of motionof the disc assembly remains centrally located between the vertebralbodies, similar to the centroid of motion in a healthy naturalintervertebral disc.

[0124] While there has been described and illustrated specificembodiments of an artificial disc, it will be apparent to those skilledin the art that variations and modifications are possible withoutdeviating from the broad spirit and principle of the invention. Theinvention, therefore, shall not be limited to the specific embodimentsdiscussed herein.

What is claimed is:
 1. An intervertebral spacer device, comprising: first and second plates, said plates being disposed in a spaced apart relationship such that a plate surface of said first plate faces a plate surface of said second plate, said facing surfaces being inner surfaces, and alternative faces of each plate being outer surfaces; and at least one restoring force providing element disposed between the inner surfaces of said first and second plates, and disposed such that a compressive load applied to the outer surfaces of said first and second plates is counteracted by said at least one restoring force providing element, said at least one restoring force providing element including at least one wave washer selected from the group consisting of a conical-shaped wave washer, a semispherical-shaped wave washer, and a wave washer having two wide ends separated by a narrower centrally bored portion from which an upwardly extending circumferential extent portion extends to form one of the wide ends and from which a downwardly extending circumferential extent portion extends to form the other of the wide ends.
 2. The intervertebral spacer device of claim 1, wherein at least one of said first and second plates comprises a post mounted to its inner surface, the post having a plurality of laterally extending spokes, and the at least one wave washer is secured to the at least one of said first and second plates with a circumferential extent of the at least one wave washer being maintained between the spokes and the at least one of said first and second plates.
 3. The intervertebral spacer device of claim 1, wherein at least one of said first and second plates comprises a flanged fastener mounted to its inner surface, the flanged fastener having a post portion and a flanged portion, and wherein the post portion has a diameter smaller than a diameter of a central bore of the at least one wave washer, and a length greater than a thickness of a portion of a circumferential extent, of the at least one wave washer, surrounding the central bore, and wherein the flanged portion has a diameter greater than the diameter of the central bore, and wherein the at least one wave washer is secured to the at least one of said first and second plates with the circumferential extent portion surrounding the central bore being maintained between the flanged portion and the at least one of said first and second plates.
 4. The intervertebral spacer device of claim 1, wherein the at least one wave washer has a circumferential extent thickness that is radially varying.
 5. The intervertebral spacer device of claim 1, wherein the at least one wave washer has a circumferential extent that is radially wavy.
 6. The intervertebral spacer device of claim 1, wherein the at least one wave washer has a circumferential extent that has at least one concentric groove.
 7. The intervertebral spacer device of claim 6, wherein the at least one concentric groove has a depth and a width, and wherein at least one of the width and the depth varies along a length of the concentric groove.
 8. The intervertebral spacer device of claim 1, wherein the at least one wave washer has a circumferential extent having at least one radially extending wave valley having a depth and a width, and wherein at least one of the depth and the width of the valley radially varies.
 9. The intervertebral spacer device of claim 1, wherein the at least one wave washer comprises a central bore and a doubled circumferential extent extending from the central bore, the doubled circumferential extent having the upwardly extending circumferential extent portion and the downwardly extending circumferential extent portion.
 10. The intervertebral spacer device of claim 9, wherein at least one of the portions is conical-shaped.
 11. The intervertebral spacer device of claim 9, wherein at least one of the portions is semispherical-shaped.
 12. An artificial intervertebral disc, comprising: first and second plates disposed to provide opposed respective inwardly facing support surfaces of said plates, and to provide respective outwardly facing vertebral body contact surfaces of said plates; and at least one wave washer disposed between the inwardly facing support surfaces such that a compressive load applied to the outwardly facing vertebral body contact surfaces is resisted by said at least one wave washer; wherein said at least one wave washer includes a central bore forming a curvate socket; and wherein at least one of said first and second plates includes on its inwardly facing support surface a semispherical protuberance that is rotatably and angulatably couplable to the curvate socket such that the plates are rotatable and angulatable relative to one another thereby.
 13. The artificial intervertebral disc of claim 12, wherein the semispherical protrusion comprises a radially deflectable semispherical portion and the curvate socket has an interior volume and an opening leading to the interior volume, the curvate socket accommodating the semispherical portion for free rotation and angulation therein, the semispherical portion fitting through the opening only when radially deflected, the semispherical portion being adapted to receive a deflection preventing element that when applied to the semispherical portion prevents the semispherical portion from fitting through the opening.
 14. The artificial intervertebral disc of claim 13, wherein the semispherical protuberance comprises at least one radial slot such that the semispherical protuberance is radially deflectable upon the application of a radially inwardly directed force.
 15. The artificial intervertebral disc of claim 14, wherein the semispherical protuberance further comprises an axial bore into which the deflection preventing element is disposable to prevent the radial deflection of the semispherical protuberance.
 16. The artificial intervertebral disc of claim 12, wherein said at least one wave washer is selected from the group consisting of a ring-shaped wave washer, a spiral-shaped wave washer, a conical-shaped wave washer, and a semispherical-shaped wave washer.
 17. An artificial intervertebral disc, comprising: first and second plates disposed to provide opposed respective inwardly facing support surfaces of said plates, and to provide respective outwardly facing vertebral body contact surfaces of said plates; and at least one wave washer rotatably coupled to the inwardly facing support surface of at least one of said first and second plates by a wave washer securing element such that the plates are made rotatable relative to one another thereby, and such that a compressive load applied to the outwardly facing vertebral body contact surfaces is resisted by said at least one wave washer.
 18. The artificial intervertebral disc of claim 17, wherein the wave washer securing element comprises a post having at least one laterally extending spoke, and said at least one wave washer is secured to the at least one of said first and second plates with a circumferential extent of said at least one wave washer being maintained between the at least one laterally extending spoke and the at least one of said first and second plates.
 19. The artificial intervertebral disc of claim 17, wherein the wave washer securing element comprises a flanged fastener having a post portion and a flanged portion, and wherein the post portion has a diameter smaller than a diameter of a central bore of said at least one wave washer, and a length greater than a thickness of a portion of a circumferential extent of said at least one wave washer surrounding the central bore, and wherein the flanged portion has a diameter greater than the diameter of the central bore, and wherein said at least one wave washer is secured to the at least one of said first and second plates with the circumferential extent portion surrounding the central bore being maintained between the flanged portion and the at least one of said first and second plates.
 20. The artificial intervertebral disc of claim 17, wherein said at least one wave washer is selected from the group consisting of a ring-shaped wave washer, a spiral-shaped wave washer, a conical-shaped wave washer, and a semispherical-shaped wave washer. 